东胜铀矿床和钱家店铀矿床后生蚀变特征及其与铀成矿关系

东胜铀矿床和钱家店铀矿床后生蚀变特征及其与铀成矿关系
　　Dongsheng and Qianjiadian uranium deposits are two sandstone-type uranium deposits discovered in China in recent years and have unique characteristics of the epigenetic alteration zones. The two deposits have been studied in detail mainly focusing on petrologic, mineralogical and geochemical characteristics of their epigenetic alteration zones. Compared with typical interlayer-oxidation zone sandstone uranium deposits, the relation of their epigenetic alteration to the uranium mineralization has been discussed providing for uranium metallogenic prognosis.Observing under the microscope and electron probe microanalysis and SEM reveal that the uranium-hosting sandstone of the lower member of Zhiluo Formation in Dongsheng uranium deposit is lithic-feldspar sandstone and main alteration minerals are smectite, chlorite, epidote, calcite, limonite, pyrite, coffinite, etc; the uranium-hosting sandstone of Yaojia Formation in Qianjiadian uranium deposit is feldspathic litharenite and main strong magnets alteration minerals are kaolinite, calcite, limonite, pyrite, pitchblende, ect.Macroscopical observations and microcosmic studies of the epigenetic alteration zones of Dongsheng and Qianjiadian uranium deposits reveal that their epigenetic alteration zones are slightly different from those of the typical interlayer-oxidation zones. The unique gray-green epigenetic alteration zone of Dongsheng uranium deposit is mostly composed of gray-green and green sandstones, and alteration minerals are dominantly chlorite. It is considered that the gray-green epigenetic alteration zone is the product due to the alteration by the introduced fluids in the late stage, and maybe a part of the paleo-interlayer oxidation zone.
　　The unique bleached zone of Qianjiadian uranium deposit is mostly composed of gray-white sandstones closely related to the uranium mineralization, and alteration minerals are dominantly kaolinite. It is proposed that the bleached zone is the product due to the alteration by the acidic weak-oxidizing fluids, and is a part of the interlayer oxidation zone. Main reasons for the bleached sandstone in the color of white are transfer of Fe2+, oxidation of TOC and kaolinization of sandstone.The distribution characteristics of major elements, minor elements and REE in sandstone of different geochemical types in Dongsheng and Qianjiadian uranium deposits are basically found. Compared with the gray sandstone in Dongsheng uranium deposit, the gray-green sandstone is characterized http://www.chinamagnets.biz by lower contents of TOC, S, and CaO, and slightly higher content of Al2O3,ΣREE and U, and higher ratio of LREE/HREE, and lower ratio ofΔFe2O3/FeO, ect. Compared with the gray sandstone in Qianjiadian uranium deposit, the bleached sandstone is characterized by lower contents of TOC, S, CaO andΣREE, and higher contents of SiO2, Al2O3 and U, and higher ratios of LREE/HREE andΔFe2O3/FeO, ect.Field investigations in the study area, and petrologic and mineralogical observations under the microscope and some analyses reveal that the epigenetic alteration of Dongsheng uranium deposit can mainly be divided into three types: interlayer oxidation, reducing sulfide alteration, reduction of oil-gas. Hower ,that of Qianjiadian uranium deposit can mainly be divided into two types: interlayer oxidation and reducing sulfide alteration. The epigenetic oxidation is the important condition for the migration and enrichment of uranium, while the reducing geochemical barrier composed of the epigenetic and original reduction is the key factor that uranium for the precipitation of uranium to form a deposit, and it is also the important condition for the preservation of uranium deposits.